After graduation from West Point, Gabriel entered pilot training at Goodfellow Air Force Base, Texas, and completed advanced training at Craig Air Force Base, Alabama, in December 1951. His first assignment was to South Korea, where he flew 100 combat missions in F-51 Mustangs and F-86 Sabres and was credited with shooting down two MiG-15s. From December 1952 to November 1955, Gabriel was assigned to the 86th Fighter-Interceptor Wing, Landstuhl Air Base, Germany, as a pilot and later a squadron air operations officer. He then spent three years as an air officer commanding at the United States Air Force Academy, Colorado. In July 1959, Gabriel transferred to Moody Air Force Base, Georgia, where he served as adjutant for the 3550th Pilot Training Group and commander of the Headquarters Squadron Section. Following graduation from the Naval War College in August 1962 and completion of his master's degree at George Washington University in August 1963, he was assigned as a staff officer in the Directorate of Plans, Headquarters U.S. Air Force, Washington, D.C. In August 1966 he entered the Industrial College of the Armed Forces. Returning to Europe in August 1967, Gabriel served as executive officer to the chief of staff, Supreme Headquarters Allied Powers Europe, Mons, Belgium. He returned to the United States for combat crew training in July 1970 and was subsequently assigned as commander of the 432nd Tactical Reconnaissance Wing at Udon Royal Thai Air Force Base, Thailand, flying 152 combat missions in F-4 Phantom IIs. While wing commander he accepted orders from General John D. Lavelle to falsify classified operations reports. General Lavelle was forced to retire because of these orders. He returned to the Air Staff in July 1972, as deputy for operational forces and deputy director of operations. Gabriel served as deputy chief of staff for operations at Headquarters Tactical Air Command, Langley Air Force Base, Virginia, from February 1975 to August 1977. He then became deputy commander in chief, U.S. Forces Korea and deputy commander in chief, United Nations Command, Seoul, South Korea. In April 1979, Gabriel returned to Air Force headquarters as deputy chief of staff for operations, plans and readiness. He served as commander in chief, United States Air Forces in Europe and commander of Allied Air Forces Central Europe at Ramstein Air Base, Germany, from August 1980 to June 1982. Gabriel was promoted to general on August 1, 1980, and retired on July 1, 1986. Gabriel died in Arlington County, Virginia, of Alzheimer's disease, on September 4, 2003. He is buried at Arlington National Cemetery.
